Two-way stretch paper in insulated cables



Aug- 19, 1952 G. cAMlLLl ETAL TWO-WAY STRETCH PAPER IN INSULATED CABLESFiled Deo. 2l, 1950 2 SHEETS- SHEET l .1. un... hr.. 2

Al1g 19, 1952 G. cAMlLLl Erm. 2,607,824

TWO-WAY STRETCH PAPER 1N INSULATED CABLES Filed Dec. 21, 1950 2SHEETS-SHEET 2 Invenovssh Guglieimo CamiiIig Leo'lvluiigan,

- Their' ttorne.

Patented Aug. 19, 1952 TWO-.WAYVSTRETCH PPERI'INSULA-TED CABLESGuglielmo camini, Pittsfield, and Leo Mulligan West Stockbridge, Mass.,Vassignors to'General Electric Company, a corporation of New YorkpplicationDecember 21, 1950,:Seria1N0. 202,075

, 4 Claims.

lThis-'invention relates to electrical cables and,

` more particularly, tol crepe paper insulation Vfor fs'uch' cables.

` 'In certain applications KYwhere'electrical cables v4'are used, it isdesirable to have a Cablecapable `ofi/being*subjected to ysharp-bends.For example, in the internal connections of an electricaltrans- Aformer,it is Vsometimes desirableto subject y-a cable `to sharp Vbendsapproaching a bending radius 'of two times-the diameterY of vrthecable.v

However, such an extremely sharp curvature of bending `exceeds inseverity by a Yconsiderable Amargin `concepts prevalent inthe -cableindustry regarding maximum permissible sharpness of bending.

'It lis an object tofthis inventionto provide a new andvimprovedinsulation for electrical 'cables which will permit such cablestobe bent into curvaturesof small radius.

n is 'a further @ejector nimm-entren to prf 'vide a paper insulationfor' an electrical lcable kcapable `of yielding in several' directions.

-'In accomplishment of these objectives, this 'inventionjprovidesanelectrical cable-for high voltage Vinstallations "havingr a kpluralityof )layers of crepe paper insulation' spirallywoundfabout the conductormember, with the crepepaperbeying'fprovided with two crepings 'which aresubstantially perpendicularto one another.

` The' features ofthis invention which We believe to be novel are setforth with particularity iin the appended claims.A Ourinvention,however, both as 'toits organization and use, togetherwith furtherobjects 'and Vadvantages thereofjmay best 'b'ennderstood by reference tothe ffoll'owingdescription taken nin connection with the accom- 'panyingdrawing in which Fig. 1 represents `a portion of .a 'cable incorporatingtwo-*way stretch crepe paper' 'insulation iny accordancev with our"inventi`on;`F-ig. '2 vis a viewcf a vc'able'bent to a `smallradius;Fig. `3 represents "a" detail view of *the two-'way stretch crepe paper"used in acjscorda-nce vwith our invention; "Figa l 'and 5 are^views'ofa one-waystretch crepep'aper having kReferring jnow 'to thedrawing, there 'is "shown in Fig. 1 a cable `l jwith a 'multi-strand'copper `conducting core 2 having Wound'thereon 'a Ypiuvrality vofylayers 'of our two-way `stretch crepe paper insulation 3. A braided,ber or cloth 'sheath '4 of "any suitable typelserves as "en 'outerprotective 'covering for the cable. It shouldjbe "noted that the crepepaper tape is theonly layl ered or^solid insulating medium surroundingthe conductor, with the ber cover 4 serving only as anabrasion-resistant covering Awhich is thin in a radial direction ascompared to the radial thickness of 'the superposed layers of crepevpaper insulation.

In accordance with our invention, `the crepe paper insulation `which isspirally wound around "thecopper conductor '2 is inthe form of' a 'tape'ofl crepe paper having positioned thereon two 'crepings which aresubstantially perpendicular to one another. The use ofsuchtwo-wa'y'stretch crepe paper :permits the crepe paper insulation to'readily adapt itself when the 'cable isbent into turns of as'hortradius.

Referring to Fig. 2, which' shows a Short length of cable which is bentto a radius R, it will be seen that when a paper insulated cable is`vbent to a radius R, the fibers of the paper which .lie ion theoutside ofthe curve will be stretched and those which lie on the inside Will'becompressed. If the length of cable corresponding to an angle ais'considered, the length measured along the axis of the cable willbe'Ra and the length on the outside surface will be 4(R-]-r)ll, where 1'is the radius of the cable. Thus, it will be seenl that the elongationwhich the .paper has to withstand on la length Re is ra.' The.percentage of elonga- 'tion will be times 100 Ordinary manila paperwill elongate two 'per cent before breakdown. From-this,` it maybeconclu'ded that a cable insulated With ordinary manila paper shouldnot be bent to Va radius smaller than that given by r v R tunes l00-2 inwhich case R=r. It can, therefore, be said l.that when ordinary manilapaper is used inthe making of a cable theradiusof curvature should notbe smaller than 25 times the diameter of the cable.

`In applying -a paper tape 'insulation abolita conductor, such as acrepe paper tape, the tape is wound spirally about the conductor, withthe winding angle 'of the paper tape with respect to the axis of thecable being designated as the 'angle "of lay. In accordance with 'thestandard cable, the 'cable is advanced axially 'at a constant While forany particular angle of lay there` y is a corresponding ideal angleat'which the crepe,` lines on one-way stretch crepe paper could beVarranged on the paper in order to provide maximum flexibility forbending, this ideal creping angle changes with each succeeding layer of.

crepe paper insulation, due to the change in angle of lay as the cablebecomes greater in' A further advantage of the usel of two-way,

stretch crepe paper insulation is that the crosscreping, due to the twocrepings arranged mutually perpendicularly to each other, resists` atendency to interlock, Ywhich sometimes occurs between adjacent layersof one-way stretch crepe:

paper. Such interlocking of the crepe lines on adjacent layers isundesirable, since it reduces -the fiexibility of the cable.

In Fig. 3, we have illustrated a single crepe paper tape being appliedto Va cable, with the angle of lay in this particular layer being equalto- 0. In accordance with our invention, the crepe paper which is usedhas two crepings which are substantially perpendicular to each other,and in this case, the two crepings are inclined at an angle ofsubstantially 45 degrees to the axis Vof the tape. In connection withFig. 3, there is shown a graphical analysis of the elongation whichoccurs when the cable is bent, and the components into which thiselongation may be split. The elongation parallel to the axis of thecable is designated by the vector A. The elongation A can be split upinto two components which are respectively parallel to the twodirections of creping, these two components being designated as B and C,respectively. Elongation vector A is equal to the vectorial sum of therespective component elongations B and C. It can be shown that the angleincluded between vectors A and 3:45 degrees -5- while the angle includedbetween vectors A and C':45 degrees-0. Furthermore, the value of vectorB:A cos (45 0) while vector C:A sin (45 6).

In the particular case illustrated in Fig. 3, the per cent stretch ofwhich the crepe paper should be capable is provided by the followingformulae:

Per cent stretch in direction B=T 100 cos (45 +9) Per cent stretch indirection C='- 100 sin `(45{6) 4 by the above formulae in order topermit satisfactory bending of the cable.

These relations can be stated in a more general way by the followingequations:

Per cent stretch in direction B= cos (wl-0) Per cent stretch indirection 0:?2- 100 sin (w-i-) Where r:radius of the insulated cableR:radius of curvature of the cable w:angle of creping from the axis ofthe strip of paper :angle of lay used in the insulation of the cable.

To illustrate the advantage of the use of twoway stretch crepe paperover conventional crepe paper having crepe lines in only one direction,there is shown in Figs. 4 and 5 a crepe paper tape for insulating acable in which the crepe lines are perpendicular to the axis of thetape. In Fig. 4, the tape is shown woundlperpendiculai-ly to the axis ofthe cable.r It is evident in this case thatthere is absolutely noadvantage in using a crepe paper having crepe lines perpendicular to theaxis of the tape over the use of un- ,creped paper, since the crepelines are in the wrong direction insofar as yielding is concerned. Inthe embodiment shown `in Fig. 4, the crepe paper will not stretch atall, since the crepe lines are parallel to the axis of the cable andhaveno component perpendicular Yto the axis of the cable. However, inpractice, the paper iswound spirally on the conductor, asshown in Fig.5, and the angle of lay 0 may b e of the order of between 15 and l20degrees. Assuming thatv the angle of lay is 20 degrees in Fig. 5, itwill be seen that in order to avoid breaking the paper, both 'componentsB and C of elongation A should be taken care of. For 0:20degrees,cornponent B:.94A, and component C:.34A. In the casek of theoneway stretch crepe vpaper shown in Figs. 4 and 5, the component -B isnot taken care of at all, since there are' no crepe lines which permitelongation in the direction of B.

ThereA is shown in Figs'. 6 and 7 a tape having crepe lines parallel tothe axis of the tape. In Fig. 6, the tape is shown wound perpendicularlyto the axis` of the cable. If the paper could 'be wound, as shown inFig. 6, with the type of creping shown in that ligure, very satisfactoryresults -could be obtained without any further complications, since thealignment of the crepe lines is perpendicular to the axis of cable and,hence, capable of yielding axially of the cable when the cable is bent.However, in practice, the paper must be Ywound with an angle of lay 0,as shown in Fig. 7, and in order to avoid breakage of the paperwhenthecable is bent both components B and C must be taken care of. Assumingthat the angle of lay is 20 degrees, to avoid breakage of the paper itis necessary that the paper be Vprovided with two stretches: rst, with astretch 'perpendicular to the axis rof the paper tape, represented bycomponent B, equal to not less fth'an 94 per cent of the elongation ofthe outside -surface of the bent cable, and an additional stretchalongthe axis of the paper, represented by component C, equal to 34 percent of the elongationfof the outside surface of the bent cable. v' Theone-way stretch crepe paper of Fig. 7 is not provided with acreping'capable of yielding indiv'rection C.' 1 f.' flfakentogethenFigs.4, 5,6, and 'Iv showY that crepe paper tape having creping lines in onlyone direction, whether that direction be perpenfdicular to the axis ofthe tape or parallel to the axis of the tape is insufficient to permitsharp cable bends.

Our cable having two-way stretch crepe paper insulation is capable ofwithstanding sharp cable bends having a radius of curvature of the orderof two times the diameter of the cable. Furthermore, a two-way stretchcrepe paper insulation such as we have disclosed adapts itself readilyto the change in angle of lay which occurs as successive layers of crepepaper are wound on the cable and resists interlocking between the crepelines of adjacent layers.

While we have illustrated an embodiment of our invention in which themutually perpendicular crepe lines of our two-way stretch crepe paperinsulation are arranged at an angle of 45 degrees with respect to theaxis of the crepe paper tape, it is obvious that we may shift theposition of our crepe lines with respect to the axis of the tape. Forexample, one of the crepings may be parallel to the axis of the tape andthe other creping may be perpendicular to the axis of the tape.

While there has been shown and described a particular embodiment of ourinvention, it will be obvious to those skilled in the art that variouschanges and modications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electrical cable including an electrical conductor, and aplurality of layers of crepe paper tape spirally wound about saidconductor, said spirally-wound crepe paper tape advancing longitudinallyalong the axis of said conductor, said crepe paper tape having twocrepings substantially perpendicular to each other so that eachindividual layer of said crepe paper tape can stretch in two directions.

2. An electrical cable including an electrical conductor, and aplurality of layers of crepe paper tape spirally wound about saidconductor,

said spirally-wound crepe paper tape advancing longitudinally along theaxis of said conductor, said crepe paper tape having two crepingssubstantially perpendicular to each other so that each individual layerof said crepe paper tape can stretch in two directions, 'each of saidcrepings making an angle of substantially 45 degrees with respect to theaxis of said tape.

3. An electrical cable comprising an electrical conductor, and aplurality of layers of crepe paper tape spirally wound about saidconductor, said spirally-wound crepe paper tape advancing longitudinallyalong the axis of said conductor, said crepe paper tape having twocrepings substantially perpendicular toV each other so that eachindividual layer of said crepe paper tape can stretch in two directions,one of said crepings being substantially parallel to the axis of saidtape, and the other of said crepings being substantially perpendicularto the axis of said tape.

4. An electrical cable including an electrical conductor, a plurality oflayers of crepe paper tape spirally wound about said conductor, saidspirally-wound tape advancing longitudinally of the axis of saidconductor. said crepe paper tape having two crepings substantiallyperpendicular to each other so that each individual layer of said crepepaper tape can stretch in two directions, and a protective sheathcovering the outermost layer of said crepe paper, said crepe paper andsaid sheath constituting substantially the only solid coveringssurrounding said conductor.

GUGLIELMO CAMILLI. LEO MULmGAN.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 2,045,103 Rosch June 23. 19362,071,347 Kemp Feb. 23, 1937 FOREIGN PATENTS Number Country Date 19,951England Sept. 7. 1901

